Illumination apparatus

ABSTRACT

A point light source is converted into a plane light source having a satisfactory uniformity. The point light source is converted into a line light source by means of a linear light guiding plate, and further into the plane light source by means of a plane-like light guiding plate. Light from the point light source is reflected at a lamp reflector to be incident on at least two side surfaces of the plane-like light guiding plate.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an illumination apparatus forilluminating an image display plane of a liquid crystal display device,and more specifically, relates to a scheme intended to realize a uniformin-plane brightness of the illumination apparatus in a method forconverting a point light source into a plane light source. By means ofthe present invention, an illumination apparatus capable of emittinglight as a plane light source with no unevenness in brightness can berealized even when a point light source is employed. In addition, bymeans of the present invention, an illumination apparatus capable ofemitting light as a plane light source with less unevenness inbrightness can be realized even when the small number of point lightsources is employed.

2. Description of the Related Art

A liquid crystal electro-optical device is widely used in view ofadvantages of low power consumption, light weight, and a smallthickness. The liquid crystal electro-optical device includes adirect-view type liquid crystal electro-optical device and aprojection-type liquid crystal electro-optical device. In the case of adirect-view and transmission type liquid crystal electro-optical device,a viewer recognizes an image by means of a back light. In the case of adirect-view and reflection type liquid crystal electro-optical device, aviewer recognizes an image by means of a front light.

FIG. 22 shows a perspective view of an edge-light type back light inwhich light sources are disposed at side surfaces of a plate-like lightguiding plate. More specifically, the light sources 104, each of whichis a line light source such as a cold cathode fluorescent tube or thelike, are provided at two opposite side surfaces of the plate-like lightguiding plate 105. Light incident onto the plate-like light guidingplate 105 is scattered by means of ink dots 106 formed on a rear surfaceof the plate-like light guiding plane to emit toward a transmission typeliquid crystal electro-optical device 101. A prism sheet 103 may be usedover the plate-like light guiding plate in order to enhance brightnessin the front direction. Light emitted from the plate-like light guidingplate and provided with directionality by means of the prism sheet isincident on a diffusion plate 102 so that the in-plane brightnessdistribution can become uniform by means of the diffusion plate. Lightscattered by the ink dots and leaked downward from the plate-like lightguiding plate is reflected by reflecting plate 107 to travel back towardthe liquid crystal electro-optical device 101.

Thus, the illumination apparatus such as a back light is provided with aplate-like light guiding plate disposed below a display region of aliquid crystal electro-optical device, and further provided with linelight sources disposed at the side surfaces of the plate-like lightguiding plate. Light emitted from the light sources repeats totalreflections within the plate-like light guiding plate to be expandedover the entire region of the plate-like light guiding plate. FIGS. 20Aand 20B respectively show cross-sectional views of the plate-like lightguiding plate in the thickness direction thereof, illustrating differentmanners of light propagation in the plate-like light guiding plate. Itshould be noted that six surfaces are defined for the plate-shaped lightguiding plate as shown in a perspective view of FIG. 19A, in order toexplain the light propagation. More specifically, a surface closer to aviewer is referred to as an upper surface 735, while a surface oppositeto the upper surface is referred to as a lower surface 736. A sidesurface onto which a light emitted from a light source 737 is incidentis referred to as an end surface 738. Each of surfaces perpendicular tothe end surface is referred to as a side surface 739. The last surfaceis a surface 740, which is parallel to the end surface.

FIG. 20A illustrates the light propagation in the case where light isincident along the end surface 109 of the plate-like light guiding platehaving the refractive index of 1.49 from the air 112 having therefractive index of 1. The light incident along the end surface of theplate-like light guiding plate is refracted in accordance with theSnell's law to be propagated at the angle of 42° with respect to thenormal direction of the end surface of the plate-like light guidingplate, and is then incident on the lower surface 110 of the plate-likelight guiding plate at the angle of 48° which exceeds the criticalangle, thereby being totally reflected. Thereafter, the light isincident on the upper surface 111 of the plate-like light guiding plateat the angle of 48° to be totally reflected. Thus, the light repeats thetotal reflections at the upper surface 111 of the plate-like lightguiding plate and the lower surface of the plate-like light guidingplate. FIG. 20B illustrates the light propagation in the case wherelight is incident at the angle (θ₁) smaller than 90° with respect to thenormal direction of the end surface 109 of the plate-like light guidingplate 105 having the refractive index of 1.49 from the air having therefractive index of 1. The light entering the plate-like light guidingplate is incident on the upper surface 111 of the plate-like lightguiding plate and the lower surface 110 of the plate-like light guidingplate at the angle (θ₂), which exceeds the critical angle. Thus, thelight repeats the total reflections at the upper surface of theplate-like light guiding plate and the lower surface of the plate-likelight guiding plate, thereby resulting in the light being emitted fromthe surface parallel to the end surface 109 while being inclined at theangle of θ₁ with respect to the normal direction of this surface.

Thus, the light incident on the end surface 109 of the plate-like lightguiding plate at any angle is entirely totally reflected within theplate-like light guiding plate. Accordingly, no light is allowed to emitthrough the upper surface of the plate-like light guiding plate or thelower surface of the plate-like light guiding plate, so long as nostructural member is provided at the upper or lower surface of theplate-like light guiding plate. In addition, as calculated from theSnell's law, the light incident from the air onto the end surface of theplate-like light guiding plate at any angle is refracted at theinterface between the air and the end surface of the plate-like lightguiding plate, so that the light propagating within the plate-like lightguiding plate is inclined with respect to the normal direction of theend surface of the plate-like light guiding plate at 42° or less.

In the case where it is desired to emit the light through the uppersurface of the plate-like light guiding plate, white-colored ink dotsmay be provided at the lower surface of the plate-like light guidingplate. FIG. 23 illustrates a cross-sectional view of an edge-light typeback light. Like reference numerals designate like components both inFIGS. 22 and 23. A light source 104 is provided in the vicinity of anend surface 109 of the plate-like light guiding plate, and a lampreflector 108 is formed around the light source. Light emitted from thelight source and light reflected from the lamp reflector are allowed toenter a plate-like light guiding plate through the end surface of theplate-like light guiding plate 105. The light is incident on the uppersurface 111 of the plate-like light guiding plate and the lower surface110 of the plate-like light guiding plate to be totally reflected withinthe plate-like light guiding plate. However, since the white-colored inkdots 106 are printed on the lower surface of the plate-like lightguiding plate, the light incident onto the ink dots 106 is scattered dueto the shape or the refractive index of the ink dots. When the light isthus scattered by the ink dot and is allowed to be incident on the uppersurface 111 of the plate-like light guiding plate at the angle smallerthan the critical angle, the light is allowed to exit from theplate-like light guiding plate. Thus, by optimizing the size, the pitchand the density of the ink dots, the in-plane brightness of the lightexiting the plate-like light guiding plate can be made uniform.

The illumination apparatus in which the light is emitted through thelower surface of the plate-like light guiding plate can be applied to afront light of a reflection type liquid crystal electro-optical device.In the case of the direct-view and reflection type liquid crystalelectro-optical device, a display region of the reflection type liquidcrystal electro-optical device is irradiated with the illumination fromthe front light, so that a viewer can recognize an image. The frontlight is lit under the small amount of external light so that the imagecan be easily viewed.

FIG. 24A illustrates a cross-sectional view of a prism-type front lightas one example of the front light. A plate-like light guiding plate 202provided with a prism surface on its upper surface is formed over adisplay region of a reflection type liquid crystal electro-opticaldevice 201. Adjacent to an end surface 213 of the plate-like lightguiding plate, a light source 203 is disposed. In order to effectivelyguide the light emitted from the light source toward the end surface ofthe plate-like light guiding plate, a lamp reflector 204 is provided. Across-sectional view in FIG. 24B illustrates an operation of theprism-type front light when the light is off. When the light source isoff, external light 205 passes through the plate-like light guidingplate 202 and is then reflected from the reflection type liquid crystalelectro-optical device 201, so that the reflected light containing theimage information is emitted toward the viewer. On the other hand, across-sectional view in FIG. 24C illustrates an operation of theprism-type front light when the light is on. When the light source 203is on, light 206 emitted from the light source 203 is reflected from thelamp reflector 204 to be incident on the end surface 213 of theplate-like light guiding plate 202. The light 206 incident on theplate-like light guiding plate 202 is then surface-reflected at a sidesurface of the prism to be incident on the reflection type liquidcrystal electro-optical device 201. The light reflected from thereflection type liquid crystal electro-optical device 201 is incident onthe interface between the plate-like light guiding plate and the air atthe angle smaller than the critical angle, thereby being allowed to exitfrom the plate-like light guiding plate.

In an alternative embodiment mode of the front light of the reflectiontype liquid crystal electro-optical device, projections may be providedon the lower surface of the plate-like light guiding plate. FIG. 25Aillustrates a cross-sectional view of the projection-shape front light.On a lower surface of a plate-like light guiding plate 207, projections208 each having a rectangular cross-section are formed. The shape of theprojections is not limited to a rectangular shape, but may becorrugated. In order to effectively guide the light emitted from a lightsource 209 toward an end surface of the plate-like light guiding plate,a lamp reflector 210 is provided. A reflection type liquid crystalelectro-optical device 212 is disposed below the plate-like lightguiding plate. A cross-sectional view in FIG. 25B illustrates anoperation of the projection-shape front light when the light is off.When the light source is off, the external light 211 passes through theplate-like light guiding plate 207 and is then reflected from thereflection type liquid crystal electro-optical device 212 to be emittedtoward the viewer. On the other hand, a cross-sectional view in FIG. 25Cillustrates an operation of the projection-shape front light when thelight is on. When the light source 209 is on, the light 213 emitted fromthe light source 209 is reflected from the lamp reflector 210 to beincident on the end surface 207 of the plate-like light guiding plate.When the light incident on the end surface of the plate-like lightguiding plate propagates within the plate-like light guiding plate to beincident on a bottom surface of the projection 208 formed on the lowersurface of the plate-like light guiding plate, the light is totallyreflected so as to propagate within the plate-like light guiding plate.When the light is incident on a side surface of the projection 208, thetotal-reflection condition of the light is not met so that the light isrefracted at the side surface. Most of the thus refracted light isincident on the reflection type liquid crystal electro-optical device,so that the reflected light containing the image information is allowedto emit toward the viewer. Thus, in the projection-shape front light,the total-reflection condition is not met for the light incident on theside surface of the projection provided on the lower surface of theplate-like light guiding plate, so that the light is incident on thereflection type liquid crystal electro-optical device. In order to allowthe light to be uniformly incident on the reflection type liquid crystalelectro-optical device, the projections are formed at a lower density inthe vicinity of the light source while at a higher density as furtheraway from the light source.

Since the liquid crystal electro-optical device is of the non-emissiontype, the device is used by projecting light thereto from a back lightor a front light in order to improve the visibility of a display. As alight source of the back light or the front light, a cold cathodefluorescent tube is generally used. However, when the cold cathodefluorescent tube is used as the light source, most of power consumptionof the liquid crystal display device is derived from the back light orthe front light. In order to reduce the power consumption of the liquidcrystal display device, a light emitting diode (LED) is recently used asthe light source instead of the cold cathode fluorescent tube. Use ofthe light emitting diode can suppress the power consumption to afraction of that necessary when the cold cathode fluorescent tube isused.

Since the light emitting diode is a point light source, it can have thesize of about 1 mm×1 mm and the thickness of about 2 to 3 mm. In orderto reduce the size of the liquid crystal display device, the lightemitting diode can be employed. Since the light emitting diode is apoint light source, means for converting such a point light source intoa plane-like light source having a high uniformity of in-line brightnessis required.

In an attempt where a point light source such as a light emitting diodeis converted into a plane light source so as to obtain a uniformlightness in a large area, unevenness in the brightness cannot beavoided. In an example for converting the point light source into theplane light source, as shown in a top plan view of FIG. 21 in which aplurality of point light sources 301 to 303 such as a light emittingdiode are disposed on a side surface of a plate-like light guiding plate304, light incident from the point light sources onto the plate-likelight guiding plate is expanded in a plane within the plate-like lightguiding plate. However, even when a plurality of point light sources aredisposed on the side surface of the plate-like light guiding plate,these point light sources can not be converted into a uniform planelight source. As previously explained, when an acrylic resin is used forthe plate-like light guiding plate, light is incident from the airhaving the refractive index of 1 onto the acrylic resin having therefractive index of 1.49, and therefore, refraction occurs due to adifference in refractive indices of the involved materials. As can becalculated from the Snell's law, the light refracted at the interfacebetween the air and the plate-like light guiding plate is expanded onlyup to the maximum angle (θ_(A)) of 42° with respect to the normaldirection of the incident surface of the plate-like light guiding plate.Thus, even when the light emitted from the point light sources isincident on the plate-like light guiding plate, the light is expandedonly over certain regions of the plate-like light guiding plate whilethe light is not expanded to some regions 305 therein. In the case wherethe illumination light is employed as a front light or a back light fora liquid crystal electro-optical device, the brightness on an image areahas to be uniform. With a large unevenness in the brightness, thevisibility is significantly damaged. Even when a diffusion plate isprovided between the point light sources 301 to 303, such as lightemitting diodes, and the plate-like light guiding plate 304, uniformityin the diffused light is not satisfactory so that in-plane unevenness inthe brightness is induced for the illumination light emitted from theback light or the front light.

An example of an illumination apparatus in which one point light sourceand a plate-like light guiding plate are employed is described, forexample, in Japanese Laid-Open Patent Publication No. 10-199318. In thisillumination apparatus, a point light source is disposed at the centerportion of a side surface of the plate-like light guiding plate. Morespecifically, as shown in a plan view of FIG. 31, the illuminationapparatus includes only a plate-like light guiding plate 304 and a pointlight source 307 at the center portion of a side surface of theplate-like light guiding plate, and therefore, the light of the pointlight source expanded within the plate-like light guiding plate can notspread over the entire display region, so that corner areas 306 of thedisplay region become dark.

Means for converting a point light source into a plane light source isdesirably means for obtaining a bright plane light source having asatisfactory uniform in-plane brightness. In addition, it is preferableto miniaturize an illumination apparatus for converting the point lightsource into the plane light source as much as possible. Furthermore, itis also preferable to determine the shape of the light guiding plate anda position at which the point light source is to be disposed on thelight guiding plate in light of the light usage efficiency.

SUMMARY OF THE INVENTION

In order to explain means for solving the problems, six surfaces aredefined for the plate-shaped light guiding plate as shown in aperspective view of FIG. 19A. More specifically, a surface closer to aviewer is referred to as an upper surface 735, while a surface oppositeto the upper surface is referred to as a lower surface 736. A sidesurface onto which a light emitted from a light source 737 is incidentis referred to as an end surface 738. Each of surfaces perpendicular tothe end surface is referred to as a side surface 739. The last surfaceis a surface 740, which is parallel to the end surface. The followingdescriptions with reference to FIGS. 1, 2A to 2C, and 3A to 3C are basedon the above definitions.

In accordance with the present invention, a point light source isconverted into a line light source by means of a linear light guidingplate, and further into a plane light source by means of a plane-likelight guiding plate. Thus, the plane light source having less unevennessin the brightness can be formed even when a point light source isemployed.

The present invention will be explained with reference to FIGS. 1, 2A to2C, and 3A to 3C. A perspective view in FIG. 1 illustrates anillumination apparatus in accordance with the present invention, andperspective views of FIGS. 2A to 2C indicate cut-away views forexplaining the light propagation in the illumination apparatus inaccordance with the present invention. Furthermore, cross-sectionalviews of FIGS. 3A to 3C illustrate the path of light propagating in theillumination apparatus in accordance with the present invention.Elements in FIG. 1 are the same as those in FIGS. 2A to 2C. In addition,like reference numerals indicate like components in FIG. 1 and FIGS. 3Ato 3C.

In FIG. 1, a line light source is composed of a light emitting diode401, a lamp reflector 402, a linear light guiding plate 403, and inkdots 404. There exist a reflecting plate 405, a reflecting plate 408 anda reflecting plate 415 around the linear light guiding plate 403.Although not illustrated, additional reflecting plate may be provided soas to face a surface parallel to an end surface of the linear lightguiding plate. Light emitted from the light emitting diode is convertedinto the line light source by the linear light guiding plate and then isincident onto a plate-like light guiding plate 406 to be converted intoa plane light source. The ink dots 407 are formed on a lower surface ofthe plate-like light guiding plate. The reflecting plate 408 is providedbelow the plate-like light guiding plate for reflecting the lightscattered by the ink dots 407 beneath the plate-like light guiding platetoward a viewer.

The light propagation will be described in detail below with referenceto FIGS. 3A to 3C. FIG. 3A illustrates a cross-sectional view obtainedby cutting with a plane (chain line A-A′ in FIG. 2A) perpendicular tothe side surface of the plate-like light guiding plate and parallel tothe upper surface thereof. FIG. 3B illustrates a cross-sectional viewobtained by cutting with a plane (chain line B-B′ in FIG. 2B)perpendicular to the end surface of the linear light guiding plate andperpendicular to the upper surface of the linear light guiding plate.FIG. 3C illustrates a cross-sectional view obtained by cutting with aplane (chain line C-C′ in FIG. 2C) perpendicular to the upper surface ofthe plate-like light guiding plate and parallel to the side surfacethereof.

The cross-sectional view of FIG. 3A illustrates the light propagationviewed from the above of the plate-like light guiding plate and thelinear light guiding plate. Light emitted from the light emitting diode401 is reflected at the lamp reflector 402. The light emitted from thelight emitting diode and the light reflected from the lamp reflector gointo the inside of the linear light guiding plate 403 through the endsurface 429 thereof, and propagate within the linear light guiding plate403 while repeating the total reflections therein. When the light isincident on the ink dots 404 formed on the side surface 430 in thelongitudinal direction of the linear light guiding plate 403, the lightis scattered by the ink dots so that the light is emitted from thelinear light guiding plate toward the end surface 411 of the plate-likelight guiding plate 406. It is preferable that the ink dots 404 areformed at a low density in a region closer to the light emitting diodewhile being formed at a high density in a region further away from thelight emitting diode, so that the light can be uniformly emitted throughthe side surface 431 (the light emitting surface) of the linear lightguiding plate 403.

In order to effectively utilize the light scattered toward the outsideof the linear light guiding plate by the ink dots, the reflecting plate405 is disposed at a rear position of the side surface on which the inkdots are formed. It should be noted that the reflecting plate 405 shouldnot be attached closely to the linear light guiding plate 403. In otherwords, the linear light guiding plate 403 is required to contact theair. This is because the light entering the linear light guiding plateis required to travel in the inside of the linear light guiding platewhile repeating the total reflections therein. The reflectance of thetotal reflection is almost 100%, and therefore, there is no energy lossinvolved. On the other hand, in the case where light is reflected on ametal surface such as silver or the like, the reflectance is about 90%.When light is reflected at the metal surface, a small amount of currentflows in the metal and the current is then converted into heat, whichresults in an energy loss. Accordingly, when light is repeatedlyreflected at the metal surface, a significant loss of energy isgenerated. In view of the above, the light is required to propagatewhile repeating the total reflections within the linear light guidingplate, and therefore, the reflecting plate 405 is disposed so as not toclosely contact the linear light guiding plate.

In FIG. 3A, light is incident on the end surface 411 of the plate-likelight guiding plate 406 at an arbitrary angle. Since the light istotally reflected at the side surfaces 409 and 410 of the plate-likelight guiding plate which are perpendicular to the end surface of theplate-like light guiding plate 406 irrespective of the angle at whichthe light is incident on the end surface 411 of the plate-like lightguiding plate 406, almost no light is emitted from the side surfaces 409and 410 of the plate-like light guiding plate. This is because nostructural member such as a prism, a projection, an ink dot or the likeis provided on the side surfaces 409 and 410 of the plate-like lightguiding plate which will break the condition for the total reflection oflight. In FIG. 3A, the light which repeats the total reflections at theside surfaces 409 and 410 of the plate-like light guiding plate isallowed to be emitted through the surface 412 parallel to the endsurface of the plate-like light guiding plate in theory. However, thelight in actual propagates three-dimensionally in the plate-like lightguiding plate, and therefore, is emitted toward a viewer by the ink dotsformed on the lower surface of the plate-like light guiding plate. Thus,the intensity of light is gradually lowered at positions further awayfrom the end surface 411 of the plate-like light guiding plate.Accordingly, only the minute amount of light can reach the surface 412parallel to the end surface of the plate-like light guiding plate.Almost no light is emitted through the side surfaces 409 and 410 of theplate-like light guiding plate and the surface 412 parallel to the endsurface of the plate-like light guiding plate.

The cross-sectional view of FIG. 3B illustrates the light propagationviewed from the side surface of the linear light guiding plate throughwhich the light is allowed to emit. Light emitted from the lightemitting diode 401 is reflected at the lamp reflector 402 to be incidenton the end surface 429 of the linear light guiding plate. The lightincident on the end surface of the linear light guiding plate 403 istotally reflected at the upper surface of the linear light guiding plateand the lower surface of the linear light guiding plate. In other words,no light is basically allowed to emit through the upper surface 413 ofthe linear light guiding plate and the lower surface 414 of the linearlight guiding plate. This is because no structural member such as aprism, a projection, an ink dot is provided on the upper surface 413 ofthe linear light guiding plate and the lower surface 414 of the linearlight guiding plate which will break the condition for the totalreflection of light. It should be noted, however, the light scattered bythe ink dots 404 shown in FIG. 3A can be emitted through the uppersurface 413 of the linear light guiding plate and the lower surface 414of the linear light guiding plate. Accordingly, it is preferable toprovide the reflecting plate 408 or the reflecting plate 415 around thelinear light guiding plate in order to effectively use the light 416leaked through the upper surface of the linear light guiding plate andthe lower surface of the linear light guiding plate. In addition, sincethe light is scattered by the ink dots to be emitted from the linearlight guiding plate toward the plate-like light guiding plate, theintensity of light is gradually lowered at positions further away fromthe end surface of the linear light guiding plate. Only the minuteamount of light can reach the surface 417 parallel to the end surface ofthe linear light guiding plate.

The cross-sectional view of FIG. 3C illustrates the light propagationviewed from the surface parallel to the end surface of the linear lightguiding plate and the side surface of the plate-like light guidingplate. Light is scattered by the ink dots 404 provided on the sidesurface of the linear light guiding plate 403 so that the light isemitted through the side surface 431 (the light emitting surface) of thelinear light guiding plate to be incident on the end surface 411 of theplate-like light guiding plate 406. The light scattered by the ink dotsis also allowed to emit through the upper surface 413 of the linearlight guiding plate and the lower surface 414 of the linear lightguiding plate. Accordingly, the reflecting plate 415 is provided overthe linear light guiding plate via an air layer and the reflecting plate408 is provided below the no linear light guiding plate via an airlayer, so that the light is reflected at these reflecting plates totravel back toward the inside of the linear light guiding plate. In FIG.3C, the light incident on the end surface of the plate-like lightguiding plate 406 at any angle propagates in the plate-like lightguiding plate 406 while repeating the total reflections at the uppersurface of the plate-like light guiding plate and the lower surface ofthe plate-like light guiding plate. It should be noted, however, thatwhen the light is incident on the ink dots 407 formed on the lowersurface of the plate-like light guiding plate, the light is scattered bythe ink dots to be emitted through the surface which is positionedcloser to the viewer (i.e., the upper surface) of the plate-like lightguiding plate. In this case, the intensity of light is gradually loweredat positions further away from the end surface 411 of the plate-likelight guiding plate. Accordingly, the ink dots 407 formed on the lowersurface of the plate-like light guiding plate 406 are provided at a lowdensity at positions closer to the end surface of the plate-like lightguiding plate while provided at a high density at positions further awayfrom the end surface of the plate-like light guiding plate, so that thelight can be emitted uniformly from the upper surface of the plate-likelight guiding plate toward the viewer.

Thus, the point light source such as a light emitting diode is convertedinto a plane light source. Since the ink dots are formed on the lowersurface of the plate-like light guiding plate, the light is emittedthrough the upper surface of the plate-like light guiding plate. Theillumination apparatus having either one of the structures asillustrated in FIG. 1, FIGS. 2A to 2C, or FIGS. 3A to 3C can be employedas a back light of a transmission type liquid crystal electro-opticaldevice, or a back light of a semi-transmission liquid crystalelectro-optical device.

As each of the linear light guiding plate and the plate-like lightguiding plate, an acrylic resin may be used.

Although the ink dots are described as means for breaking the totalreflection condition of light in the linear light guiding plate, theside surface of the linear light guiding plate positioned opposite tothe plate-like light guiding plate may be instead formed in aprism-shape. Alternatively, the side surface of the linear light guidingplate positioned closer to the plate-like light guiding plate may beformed in a projection-shape.

In order to employ the present invention as a front light of a liquidcrystal electro-optical device, the surface positioned closer to aviewer (i.e., the upper surface) of the plate-like light guiding platemay be formed in a prism-shape, instead of forming the ink dots on thelower surface of the plate-like light guiding plate. Alternatively, thelower surface of the plate-like light guiding plate may be formed in aprojection-shape. When the present invention is to be used as a frontlight of a reflecting electro-optical device, the liquid crystalelectro-optical device is disposed below the plate-like light guidingplate.

Alternatively, as means for breaking the total reflection condition oflight in the plate-like light guiding plate, a material having arefractive index different from that of the plate-like light guidingplate may be formed. Further alternatively, uneven configuration may beformed on the surface of the plate-like light guiding plate so that thelight is adjusted to be incident onto the uneven surface at an anglesmaller than the angle required for the total reflection.

Another example of the present invention will be described withreference to a perspective view in FIG. 8. In order to explain thestructure of the back light as illustrated in FIG. 8, the surfaces ofthe plate-like light guiding plate are defined as shown in a perspectiveview of FIG. 19B. More specifically, a surface closer to a viewer isreferred to as an upper surface 741, while a surface opposite to theupper surface is referred to as a lower surface 742. The remainingsurfaces are referred to as side surfaces 743.

As illustrated in FIG. 8, a point light source such as a light emittingdiode 501 is provided at, at least one of corners formed by touching twoof the side surfaces of the plate-like light guiding plate to eachother. Light emitted from the point light source such as the lightemitting diode or the like is reflected at a lamp reflector 503 formedaround the point light source to be incident onto at least two of theside surfaces of the plate-like light guiding plate, thereby resultingin the light traveling to the entire region of the plate-like lightguiding plate to be converted into a plane light source. Ink dots 504are formed on a lower surface of the plate-like light guiding plate sothat the light incident on the plate-like light guiding plate isuniformly scattered toward a viewer. The light scattered toward thelower rear direction of the plate-like light guiding plate by the inkdots 504 is reflected by a reflecting plate 505 toward the viewer. Inaccordance with the present invention, the plane light source can beformed from only one point light source such as a light emitting diodeor the like. The present invention can be employed as a back light of atransmission type liquid crystal electro-optical device. FIGS. 9A to 9Cillustrate cross-sectional views the light propagation on a surfaceviewed from a viewer in FIG. 8.

The light propagation will be described with reference to FIGS. 9A to9C. FIG. 9A illustrates a first region 506 in which the light isexpanded over the plate-like light guiding plate in the case where thelight emitted from the point light source 501 is incident only on oneside surface (a first side surface 513) of the plate-like light guidingplate 502. FIG. 9B illustrates a second region 507 in which the light isexpanded over the plate-like light guiding plate 502 in the case wherethe light emitted from the point light source 501 is incident only onanother side surface (a second side surface 514) adjacent to the firstside surface. As previously described with reference to FIGS. 20A and20B, the light incident from the air onto the side surface of theplate-like light guiding plate is expanded within the plate-like lightguiding plate, as can be calculated from the Snell's law by assumingthat the refractive index of the air is 1 and that of the plate-likelight guiding plate is 1.49. However, the region over which the light isto be expanded is defined by the maximum angle of 42° with respect tothe normal direction of the side surface of the plate-like light guidingplate on which the light is incident. Thus, as shown in FIGS. 9A and 9B,in the case where the light is incident through only one side surface ofthe plate-like light guiding plate, there exist a region over which thelight can be expanded and another region over which the light can not beexpanded.

On the other hand, as shown in FIG. 9C, in accordance with the presentinvention, light is emitted from the light emitting diode 501. The lightemitted from the light emitting diode 501 is incident onto a corner ofthe plate-like light guiding plate 502 and at least two side surfaces(the first side surface and the second side surface) of the plate-likelight guiding plate 502 into the inside of the plate-like light guidingplate. Thus, by combining the regions over which the light enteringthrough the two side surfaces can be expanded, i.e., the first region506 over which the light can be expanded over the plate-like lightguiding plate and the second region 507 over which the light can beexpanded over the plate-like light guiding plate, the light can beexpanded over the entire region of the plate-like light guiding plate.

As illustrated in FIG. 8, the ink dots 504 are printed on the lowersurface of the plate-like light guiding plate 502. When the lighttraveling in the plate-like light guiding plate 502 while repeating thetotal reflections is incident on the ink dot, the total reflectioncondition of the light is broken by the ink dot 504 so that the light isemitted toward a viewer. It is preferable that the ink dots are formedat a higher density at positions further away from the light source.Moreover, it is preferable to reduce the density of the ink dots in athird region in which the first region 506 over which the light can beexpanded over the plate-like light guiding plate and the second region507 over which the light can be expanded over the plate-like lightguiding plate in FIG. 9C are overlapped with each other.

Although the light emitting diode has been described as the point lightsource, application of the present invention is not limited to the lightemitting diode. The present invention can be widely employed as meansfor converting a point light source into a plane light source. Theplate-like light guiding plate in accordance with the present inventionmay have a shape such as a rectangular parallelepiped which hassatisfactory workability. Thus, a back light can be produced at a lowcost.

In the present specification, a point light source is referred to as alight source, as shown in a plan view of FIG. 26, in which when anillumination surface 701 of light emitted from a light source 702 isdivided by axes 703 to 706 in orthogonal two directions, the brightnessdistribution at the division position is such that a brightnessdistribution 707 of a first axis (aX) 703 is different from a brightnessdistribution 708 of a second axis (bX) 704 and a brightness distribution709 of a third axis (aY) 705 orthogonal to the first axis and the secondaxis is different from a brightness distribution 710 of a fourth axis(bY) 706.

In the present specification, a line light source is referred to as alight source, as shown in a plan view of FIG. 27, in which when anillumination surface 701 is divided by axes 711 to 716 in orthogonal twodirections, the brightness distribution at the division position is suchthat a brightness distribution 717 of a first axis (aX) 711, abrightness distribution 718 of a second axis (bX) 712, and a brightnessdistribution 719 of a third axis (cX) 713 are different from each other,while the brightness distribution 720 of a fourth axis (aY) 714orthogonal to the first through third axes, a brightness distribution721 of a fifth axis (bY) 715, and a brightness distribution 722 of asixth axis (cY) 716 become uniform to an extent which causes nopractical problem. The term “uniform” means that along the respectiveaxes in the Y direction (i.e., the fourth axis, the fifth axis, and thesixth axis) in the illumination surface, the brightness distribution iswithin the range of ±5% to ±10% with respect to an average brightnessfor the same X coordinates.

In the present specification, a plane light source is referred to as alight source, as shown in a plan view of FIG. 28, in which when anillumination surface 701 is divided by axes 723 to 728 in orthogonal twodirections, the brightness distribution at the division position is suchthat a brightness distribution 799 of a first axis (aX) 723, abrightness distribution 730 of a second axis (bX) 724, a brightnessdistribution 731 of a third axis (cX) 725, the brightness distribution732 of a fourth axis (aY) 726 orthogonal to the first through thirdaxes, a brightness distribution 733 of a fifth axis (bY) 727, and abrightness distribution 734 of a sixth axis (cY) 728 become uniform toan extent which causes no practical problem. The term “uniform” meansthat the in-plane brightness distribution is within the range of ±5% to±10% with respect to an average brightness within the illuminationsurface.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIG. 1 illustrates a perspective view of a back light in Embodiment Mode1;

FIGS. 2A, 2B, and 2C each illustrate a perspective view of a back lightin accordance with the present invention;

FIGS. 3A, 3B, and 3C each illustrate a cross-sectional view forexplaining the light propagation of a back light in accordance with thepresent invention;

FIG. 4 illustrates a perspective view of a prism-type front light inEmbodiment Mode 2;

FIGS. 5A and 5B each illustrate a cross-sectional view for explainingthe light propagation of the prism-type front light in Embodiment Mode2;

FIG. 6 illustrates a perspective view of a projection-shape front lightin Embodiment Mode 2;

FIGS. 7A and 7B each illustrate a cross-sectional view for explainingthe light propagation of the projection-shape front light in EmbodimentMode 2;

FIG. 8 illustrates a perspective view of a back light in accordance withthe present invention;

FIGS. 9A, 9B, and 9C each illustrate a cross-sectional view forexplaining the light propagation of the back light in accordance withthe present invention;

FIG. 10 illustrates a perspective view of a back light in EmbodimentMode 3;

FIGS. 11A and 11B each illustrate a cross-sectional view for explainingthe light propagation of the back light in Embodiment Mode 3;

FIGS. 12A, 12B, and 12C each illustrate a cross-sectional view forexplaining fabrication steps of a TFT in a pixel section and in a drivercircuit portion in Embodiment 1;

FIGS. 13A, 13B, and 13C each illustrate a cross-sectional view forexplaining fabrication steps of a TFT in a pixel section and in a drivercircuit portion in Embodiment 1;

FIGS. 14A and 14B each illustrate a cross-sectional view for explainingfabrication steps of a TFT in a pixel section and in a driver circuitportion in Embodiment 1;

FIG. 15 illustrates a cross-sectional view of a liquid crystalelectro-optical device in Embodiment 1;

FIG. 16 illustrates a plan view of a TFT in a pixel section inEmbodiment 1;

FIGS. 17A to 17F each illustrate a perspective view for explaining anexample of a semiconductor device in Embodiment 2;

FIGS. 18A, 18B, and 18C each illustrate a perspective view forexplaining an example of a semiconductor device in Embodiment 2;

FIGS. 19A and 19B each illustrate a perspective view for definingsurfaces of a light guiding plate in accordance with the presentinvention;

FIGS. 20A and 20B each illustrate a cross-sectional view for explainingthe light propagation of the plate-like light guiding plate;

FIG. 21 illustrates a plan view of an illumination apparatus whichemploys the conventional point light source;

FIG. 22 illustrates a perspective view of the edge-type back light;

FIG. 23 illustrates a cross-sectional view of the edge-type back light;

FIGS. 24A, 24B, and 24C each illustrate a cross-sectional view of theprism-type front light;

FIGS. 25A, 25B, and 25C each illustrate a cross-sectional view of theprojection-shape front light;

FIG. 26 illustrates a plan view for explaining the definition of thepoint light source;

FIG. 27 illustrates a plan view for explaining the definition of theline light source;

FIG. 28 illustrates a plan view for explaining the definition of theplane light source;

FIG. 29 illustrates a cross-sectional view for explaining the lightpropagation of the back light in Embodiment Mode 4;

FIG. 30 illustrates a perspective view of the back light in EmbodimentMode 1; and

FIG. 31 illustrates a plan view of an illumination apparatus whichemploys the conventional point light source.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment Mode 1

In Embodiment Mode 1, the present invention will be applied to a backlight of a transmission type liquid crystal electro-optical device.Embodiment Mode 1 will be described with reference to FIG. 1.

In order to explain Embodiment Mode 1, six surfaces of the light guidingplate are defined as shown in a perspective view of FIG. 19A. Morespecifically, a surface closer to a viewer is referred to as an uppersurface 735. A surface opposite to the upper surface is referred to as alower surface 736. A surface on which the light emitted from a lightsource 737 is referred to as an end surface 738. Surfaces perpendicularto the end surface are referred to as side surfaces 739. The other sidesurface is referred to as a surface 740 parallel to the end surface. Thefollowing descriptions with reference to FIG. 1 are based on the abovedefinitions.

A light emitting diode 401 is disposed on a first end surface 432 of alinear light guiding plate (first light guiding plate) 403. The lightemitting diode may be disposed at each of opposite ends (both on thefirst end surface and on a surface parallel to the first end surface) ofthe linear light guiding plate so that the total number thereof becomestwo.

As in a field sequential scheme, in the case where colors of lightemitted from the light source of the back light are switched at a highspeed to realize a color display, three of the light emitting diodes,i.e., a red-color light emitting diode, a green-color light emittingdiode, and a blue-color light emitting diode are provided. With thefield sequential scheme, the colors of the light sources of the backlight are switched so as to realize a color display by employing anafterimage effect of human eyes. Thus, no color filter otherwise used inthe liquid crystal electro-optical device is required, thereby resultingin a bright display being realized.

In the case where a color display is performed with a color filter inthe transmission type liquid crystal electro-optical device, awhite-color light emitting diode is preferably used as its light source.It should be noted that the white-color light can be obtainedalternatively by employing the red, green, and blue light emittingdiodes and allowing them to simultaneously emit light while adjustingthe color balance among them.

A lamp reflector 402 covers the periphery of the light emitting sectionof the light emitting diode 401 of the present embodiment mode. Thus,most of the light emitted from the light emitting diode 401 enters thelinear light guiding plate 403 through the first end surface thereof, sothat no light is leaked to the outside of the lamp reflector 402. Inaddition, the light returning from the linear light guiding plate 403toward the light emitting diode 401 is reflected at the lamp reflector402 to again travel back to the linear light guiding plate 403.

The light entering the linear light guiding plate 403 through the firstend surface thereof propagates in the inside of the linear light guidingplate while repeating the total reflections. The light is scattered byink dots 404 printed on the side surface opposite to the first sidesurface 433 which faces the plate-like light guiding plate 403, so thatthe scattered light is allowed to exit from the linear light guidingplate to be incident on a second end surface 434 of a plate-like lightguiding plate (second light guiding plate) 406.

The linear light guiding plate preferably has a rectangularcross-section. This is because the rectangular cross-section is likelyto induce the total reflection and can be easily fabricated. It shouldbe noted, however, that the linear light guiding plate may have across-section of any other shape, e.g., an elliptical cross-section, solong as the total reflection of light is realized. Moreover, a materialto be used for the linear light guiding plate may be any material, suchas an acrylic resin, so long as the total reflection of light can berealized.

In order to effectively use the light scattered by the ink dots 404 andemitted from the linear light guiding plate toward the directionopposite to the plate-like light guiding plate, a reflecting plate 405is disposed in the rear side surface of the linear light guiding plateon which the ink dots are formed. It should be noted that the reflectingplate 405 and the linear light guiding plate 403 should not be closelycontact to each other. In other words, the linear light guiding plate403 is required to contact the air.

The light scattered by the ink dots 404 is allowed to emit also throughthe upper surface of the linear light guiding plate and the lowersurface of the linear light guiding plate. Thus, the linear lightguiding plate 403 may be surrounded by a reflecting plate 405, areflecting plate 408, and a reflecting plate 415.

The ink dots 404 provided on the side surface of the linear lightguiding plate 403 will be described. If the ink dots are uniformlyprinted, portions closer to the light emitting diode become bright whileportions away from the light emitting diode become dark. Thus, the sizeand/or the density of the ink dots are varied in order to obtain auniform line light source. More specifically, in the vicinity of thelight emitting diode, the size of ink dots is reduced and/or the densitythereof is lowered so that the light is less likely to be scattered. Asfurther away from the light emitting diode, the size of the ink dots areenlarged and the density thereof is increased.

The ink dots 404 formed on the side surface of the linear light guidingplate 403 are only required to have a function of breaking the totalreflection condition and scattering the light. Thus, any structuralmember other than the ink dots, for example, a prism, a roughenedsurface, or a projection, may be provided.

Moreover, in order to diffuse the point light source to obtain a moreuniform line light source, a diffusion sheet or a lenticular lens may bedisposed between the linear light guiding plate 403 and the plate-likelight guiding plate 406.

The combination of the linear light guiding plate 403 and the lightemitting diode 401 may be disposed on up to four side surfaces of theplate-like light guiding plate. Thus, even when the point light sourceis employed, it can be converted into a line light source by means of alinear light guiding plate to obtain a uniform line light source.

Then, the plate-like light guiding plate 406 will be described below.Since the lighting system employs a back light, the ink dots 407 areprinted on a lower surface (a surface opposite to a upper surface whichis closer to a viewer) of the plate-like light guiding plate 406 inorder to allow the light incident on the plate-like light guiding plateto be scattered toward the viewer. The ink dots are desirablywhite-colored in order to effectively scatter the light.

Similarly as the ink dots formed on the linear light guiding plate, ifthe ink dots are uniformly printed on the lower surface of theplate-like light guiding plate 406, in-plane unevenness of brightness isinduced. Accordingly, in order to obtain a uniform plane light source,the size and/or the density of the ink dots are varied. Morespecifically, in the vicinity of the linear light guiding plate, thesize of ink dots is reduced and/or the density thereof is lowered sothat the light is less likely to be scattered. As further awaytherefrom, the size of the ink dots are enlarged and/or the densitythereof is increased. Thus, the point light source is converted into theplane light source to obtain a uniform back light with less in-planeunevenness of brightness.

The light guiding plate which converts a point light source into a linelight source may have a wedge-like shape in which a lateral widthbecomes narrower as further away from the point light source. FIG. 30illustrates an upper surface of an illumination apparatus of the presentembodiment mode in which a wedge-shaped light guiding plate is used asmeans for converting the point light source into the line light source.In FIG. 30, a wedge-shaped light guiding plate 1100, a plate-like lightguiding plate 1101 provided adjacent to a side surface of thewedge-shaped light guiding plate via an air layer, and a point lightsource 1103 are illustrated. In this illumination apparatus, lightemitted from the point light source is converted to be linear by meansof the wedge-shaped light guiding plate to be incident onto theplate-like light guiding plate. Accordingly, uniform brightness can beobtained in a wider area as compared to the case in which the lightemitted from the point light source is directly incident on theplate-like light guiding plate. It should be noted, however, that in thewedge-shaped light guiding plate, a component 1104 orthogonal to theplate-like light guiding plate becomes longer as one side of theplate-like light guiding plate becomes longer. In a liquid crystaldisplay device, peripheral portions of an outline except for a displayregion is referred to as a peripheral rim, and a recent trend is anarrower peripheral rim in which an area of the peripheral rim isreduced. When the wedge-shaped light guiding plate occupies a largeportion with respect to the display region, it becomes difficult torealize the narrow peripheral rim. Thus, as the light guiding plate forconverting the point light source into the line light source in thepresent embodiment mode, it is preferable to employ such a linear lightguiding plate having a constant lateral width.

Embodiment Mode 2

The present embodiment mode describes an example in which the presentinvention is applied to a front light of a reflection type liquidcrystal electro-optical device. The embodiment mode is characterized inthat a point light source by means of a light emitting diode isconverted into a line light source by a linear light guiding plate.

In order to explain Embodiment Mode 2, six surfaces of the light guidingplate are defined as shown in a perspective view of FIG. 19A. Morespecifically, a surface closer to a viewer is referred to as an uppersurface 735. A surface opposite to the upper surface is referred to as alower surface 736. A surface on which the light emitted from a lightsource 737 is specifically referred to as an end surface 738. Surfacesperpendicular to the end surface are referred to as side surfaces 739.The other side surface is referred to as a surface 740 parallel to theend surface. The following descriptions with reference to FIGS. 4, 5Aand 5B, 6, 7A and 7B are based on the above definitions.

Only points different from Embodiment Mode 1 will be described indetail. Since the present invention is applied to the reflection typeliquid crystal electro-optical device in the present embodiment mode,the plate-like light guiding plate is different from that employed inEmbodiment Mode 1. The point light source is converted into the linelight source by means of the light emitting diode and the linear lightguiding plate, as in Embodiment Mode 1.

The structure of the present embodiment mode will be described withreference to FIGS. 4, 5A and 5B, 6, 7A and 7B. A perspective view inFIG. 4 illustrates a front light in the present embodiment mode. Thelight emitted from the light emitting diode 401 is reflected at the lampreflector 402 to be incident on the end surface of the linear lightguiding plate 403 and then scattered by the ink dots 404 formed on theside surface of the linear light guiding plate toward a plate-like lightguiding plate 419. The light scattered by the ink dots 404 can be alsoemitted through the upper surface of the linear light guiding plate 403and the lower surface of the linear light guiding plate. Thus, thelinear light guiding plate is surrounded by reflecting plates 421 and422 and a reflecting plate 405 so that the light scattered by the inkdots and leaked to the outside of the linear light guiding plate isreflected to travel back to the linear light guiding plate so as toimprove the light usage efficiency.

The light emitted from the side surface of the linear light guidingplate to be incident on the end surface of the plate-like light guidingplate 419 is totally reflected by the side surface of the plate-likelight guiding plate orthogonal to the end surface of the plate-likelight guiding plate so as to be expanded throughout the inside of theplate-like light guiding plate. It should be noted that the uppersurface of the plate-like light guiding plate 419 is subjected to aspecial processing 418 so that the reflected light surface-reflected atthe upper surface of the plate-like light guiding plate 419 is incidenton a reflection type liquid crystal electro-optical device 420. Examplesof the special processing are explained with reference tocross-sectional views in FIGS. 5A and 5B. FIGS. 5A and 5B illustrateexamples of a prism-type front light in which the upper surface of theplate-like light guiding plate 419 is subjected to the specialprocessing into a prism-shape. FIGS. 5A and 5B illustrate views obtainedby cutting FIG. 4 along a chain line D-D′. FIG. 5A illustrates anoperation when the light is off. External light 423 is incident on theplate-like light guiding plate 419. The external light 423 is reflectedat a reflection type liquid crystal electro-optical device 420 so thatthe light containing image information is recognized by a viewer. FIG.5B illustrates an operation when the light is on. The light 424 emittedfrom the light emitting diode propagates in the linear light guidingplate 403 to be scattered by the ink dots 404. The light scattered bythe ink dots is incident on the plate-like light guiding plate 419. Inthis case, the light incident on the plate-like light guiding plate isconverted into the line light source by means of the linear lightguiding plate. The light is then surface-reflected by the specialprocessing 418, i.e., a prism-shape, of the upper surface of theplate-like light guiding plate to be incident on a reflection typeliquid crystal electro-optical device 420. Thus, the light containingthe image information is recognized by a viewer.

Examples in which the special processing is provided on the lowersurface of the plate-like light guiding plate will be described withreference to FIG. 6 and FIGS. 7A and 7B. A perspective view of FIG. 6illustrates a projection-shape front light in which the lower surface ofthe plate-like light guiding plate 425 is specially processed into aprojection-shape 426. The functions of the light emitting diode 401, thelamp reflector 402, the linear light guiding plate 403, the ink dots404, the reflecting plates 421 and 422, and the reflecting plate 405illustrated in FIG. 6 are the same as those explained with reference toFIG. 4. A reflection type liquid crystal electro-optical device 420 isdisposed below the plate-like light guiding plate. The light incident onthe end surface of the plate-like light guiding plate 425 is totallyreflected at the two side surfaces orthogonal to the end surface of theplate-like light guiding plate so as to be expanded entirely over theplate-like light guiding plate. The lower surface of the plate-likelight guiding plate 425 is subjected to the special processing to beprovided with the projections 426. The propagation of light incidentonto the projections formed on the lower surface of the plate-like lightguiding plate is illustrated in FIGS. 7A and 7B. The cross-sectionalviews in FIGS. 7A and 7B are obtained by cutting the perspective view ofFIG. 6 along a chain line E-E′. FIGS. 7A and 7B illustrate the lightpropagation viewed from the side surfaces of the plate-like lightguiding plate, the linear light guiding plate and the reflection typeliquid crystal electro-optical device. FIG. 7A illustrates an operationwhen the light is off. External light 427 is incident on the plate-likelight guiding plate 425 having the lower surface provided with theprojections 426. The external light 427 is reflected at a reflectiontype liquid crystal electro-optical device 420 so that the lightcontaining image information is recognized by a viewer. FIG. 7Billustrates an operation when the light is on. The light 428 emittedfrom the light emitting diode propagates in the linear light guidingplate 403 to be scattered by the ink dots 404 formed on the side surfaceof the linear light guiding plate. The light scattered by the ink dots404 is incident on the plate-like light guiding plate 425. The totalreflection condition is broken by the projections 426 so that the lightis refracted at the interface between the projections and the air to beincident on the reflection type liquid crystal electro-optical device.Thus, the light containing the image information is recognized by aviewer in the display region of the reflection type liquid crystalelectro-optical device.

Thus, in Embodiment Mode 2, the case where the present invention isapplied to a front light of the reflection type liquid crystalelectro-optical device has been described.

Embodiment Mode 3

The present invention will be described in Embodiment Mode 3. Thepresent embodiment mode is characterized by the shape of the plate-likelight guiding plate. More specifically, in the present embodiment mode,the first side surface of the plate-like light guiding plate on whichthe light is to be incident is configured to have an angle of 45° withrespect to the other side surfaces of the plate-like light guidingplate. The point light source such as a light emitting diode is disposedin front of the first side surface.

In order to explain Embodiment Mode 3, surfaces of the plate-like lightguiding plate are defined as shown in a perspective view of FIG. 19B.More specifically, a surface closer to a viewer is referred to as anupper surface 741. A surface opposite to the upper surface is referredto as a lower surface 742. The remaining surfaces are referred to asside surfaces 743. The following descriptions with reference to FIGS.10, 11A, and 11B are based on the above definitions.

FIGS. 11A and 11B illustrate cross-sectional views of an illuminationapparatus of the present embodiment mode when viewed from a viewer. Thelight propagation will be described with reference to FIGS. 11A and 11B.FIG. 11A illustrates a region 509 over which the light is expanded inthe plate-like light guiding plate in the structure in accordance withthe present embodiment mode. More specifically, the light is emittedfirst from the light emitting diode 501 disposed in front of a firstside surface 513 of the plate-like light guiding plate 502 and thenreflected at a lamp reflector 503, so that the light emitted from thelight emitting diode 501 is incident on a first side surface of theplate-like light guiding plate 502. In this case, the medium throughwhich the light is to propagate is changed from the air having therefractive index of 1 to the plate-like light guiding plate having therefractive index of 1.49. Accordingly, the light incident from the aironto the first side surface of the plate-like light guiding plate at anyangle is expanded over the region inclined against the normal directionof the first side surface at an angle of 42°. The region surelyirradiated with the light in the plate-like light guiding plate isdenoted by reference numeral 509.

FIG. 11B illustrates a cross-sectional view indicating the relationshipbetween the region 509 over which the light is expanded and a displayregion 512. The region 509 surely irradiated with the light includes therectangular display region 512. Thus, as shown in FIG. 11B, the light isexpanded over the entire display region 512. In addition, in thestructure of the present embodiment mode, the area of the light expandedto the outside of the display region is minute, so that the light usageefficiency is excellent. Moreover, since the light incident on the sidesurface of the plate-like light guiding plate at an angle smaller thanthe critical angle is leaked to the outside of the plate-like lightguiding plate, the light which does not meet the total reflectioncondition is required to be returned to the plate-like light guidingplate by a reflecting plate 511 provided around the plate-like lightguiding plate. In FIG. 11B, the reflecting plate 511 is disposed apartfrom the plate-like light guiding plate. Alternatively, a reflectingtape onto which aluminum is vapor-deposited may be adhered in closecontact to the plate-like light guiding plate.

In accordance with the present embodiment mode, the advantage ofincreasing the display region as compared to the case where the pointlight source is to be disposed at the center of the side surface of theplate-like light guiding plate can be achieved, and therefore, the areaof the peripheral rim which is not included in the display region can bedecreased so that the narrow peripheral rim of the display device can berealized. In addition, since the plate-like light guiding plate to beused in the present embodiment mode has a structure which can be easilyprocessed, the high productibility can be realized even inmass-production.

FIG. 10 illustrates a perspective view of the back light in accordancewith the present embodiment mode. As shown in FIG. 10, the ink dots 504are printed on a lower surface of the plate-like light guiding plate502. When the light propagating in the plate-like light guiding plate502 while repeating the total reflections therein is incident on the inkdots, the light is scattered by the ink dots to be emitted toward theviewer. The ink dots are preferably formed at a higher density atportions further away from the light source. A region 508 in theplate-like light guiding plate over which the light is to be expandedcorresponds to almost the entire region of the plate-like light guidingplate. In addition, the point light source 501 is disposed in front of afirst surface of the plate-like light guiding plate, and the lampreflector 503 is provided around the point light source to contact theperipheral portion of the first side surface.

Although the point light source has been described as the light emittingdiode in the present invention, application of the present invention isnot limited to such a case. For example, a midget lamp can be used asthe point light source. In the structure as shown in FIG. 10, theillumination apparatus in accordance with the present invention is usedas a back light of the transmission type liquid crystal electro-opticaldevice. By replacing the ink dots formed on the lower surface of theplate-like light guiding plate in FIG. 10 with projections having arectangular cross-section, the illumination apparatus in accordance withthe present invention can be used as a front light of a reflection typeliquid crystal electro-optical device.

Embodiment Mode 4

In the present embodiment mode, in the illumination apparatus whichconverts a point light source into a line light source and the linelight source into a plane light source, further miniaturization of theillumination apparatus will be achieved as compared to EmbodimentMode 1. The present embodiment mode will be described with reference toFIG. 29. FIG. 29 illustrates a cross-sectional view for explaining thelight propagation of a back light in accordance with the presentembodiment mode.

In order to explain Embodiment Mode 4, six surfaces of the light guidingplate are defined as shown in a perspective view of FIG. 19A. Morespecifically, a surface closer to a viewer is referred to as an uppersurface 735. A surface opposite to the upper surface is referred to as alower surface 736. A side surface on which the light emitted from alight source 737 is incident is specifically referred to as an endsurface 738. Surfaces perpendicular to the end surface are referred toas side surfaces 739. The other side surface is referred to as a surface740 parallel to the end surface. The following descriptions withreference to FIG. 29 are based on the above definitions.

A point light source 1000 is disposed in front of a first end surface1004 of a first light guiding plate (linear light guiding plate) 1001,and a first side surface of the first light guiding plate orthogonal tothe first end surface contacts a second end surface of a second lightguiding plate (plate-like light guiding plate) 1002. Although as thesecond light guiding plate, a material having the refractive index of1.4 to 1.6 can be used, an acrylic resin having the refractive index of1.49 is used in the present embodiment mode. The first light guidingplate preferably has a refractive index of 1.8 or higher in order toallow the light to be totally reflected in the first light guidingplate. However, if the refractive index of the first light guiding plateis too high, the amount of light which exits from the first lightguiding plate due to the total reflection to enter the inside of thesecond light guiding plate is reduced, and accordingly, the refractiveindex of the first light guiding plate is preferably set to be 3.0 orlower. In the present embodiment mode, the refractive index of the firstlight guiding plate is set at 2.0. Ink dots 1007 are provided on a sidesurface opposite to a first side surface which functions as a lightemitting surface of the first light guiding plate. The light incident onthe ink dots is scattered to exit the first light guiding plate, and thelight then passes through a second end surface of the second lightguiding plate to enter the inside of the second light guiding plate. Theink dots or the like are formed on the lower surface of the second lightguiding plate by a known technique, so that the light is allowed to exitthrough the upper surface of the second light guiding plate as the lightemitted from a plane light source.

The light 1003 emitted from the point light source is incident on afirst end surface 1004 of the first light guiding plate at an arbitraryangle, and is expanded in accordance with the Snell's law up to an angleof 30° at the maximum with respect to the normal direction of the firstend surface. The light further propagates to an interface 1005 betweenthe first light guiding plate and the air, and since the light isincident on the interface between the first light guiding plate and theair at an angle exceeding the critical angle, the light is totallyreflected at the interface between the first light guiding plate and theair. The light further propagates to an interface 1006 between the firstlight guiding plate and the second light guiding plate, and since thelight is incident on the interface between the first light guiding plateand the second light guiding plate at an angle exceeding the criticalangle, the light is totally reflected at the interface between the firstlight guiding plate and the second light guiding plate. In order toallow the light propagating in the first light guiding plate whilerepeating the total reflections to exit from the first light guidingplate to be incident on the second light guiding plate, the ink dots1007 are provided on a surface facing a surface at which the first lightguiding plate and the second light guiding plate contact to each other.The ink dots are preferably formed so that the density thereof becomeslower at portions further away from the point light source. A reflectingplate 1008 is preferably formed to surround the side surfaces and thelower surfaces of the first light guiding plate and the second lightguiding plate in order to allow the light leaked to the outside of thefirst light guiding plate and the second light guiding plate to bereturned toward the linear light guiding plate or the second lightguiding plate.

In Embodiment Mode 1, the first light guiding plate and the second lightguiding plate are required to be disposed via the air layer interposedtherebetween in order to allow the light to be totally reflected in thefirst light guiding plate. In contrast, in accordance with the presentembodiment mode, the light can repeat the total reflections to propagatein the first light guiding plate even when the first light guiding platecontacts the second light guiding plate, since the refractive index ofthe first light guiding plate is set to be higher than that of thesecond light guiding plate. Thus, the illumination apparatus can beminiaturized, as compared to that in Embodiment Mode 1 in which the airlayer is provided between the first light guiding plate and the secondlight guiding plate.

In accordance with the illumination apparatus of the present embodimentmode, the light from the point light source 1000 is incident on thefirst light guiding plate, and the linearly converted light is emittedfrom the first light guiding plate into the second light guiding plate,and the light converted into a plane light source is allowed to exitthrough the upper surface of the second light guiding plate.

Embodiment 1

A manufacturing method of a transmission type liquid crystalelectro-optical device to be combined with the present invention will bedescribed with reference to FIGS. 12A to 12C, 13A to 13C, 14A, 14B, 15,and 16. Like portions are designated with like reference numerals inFIGS. 12A to 12C, 13A to 13C, 14A, 14B, 15, and 16. A chain line F-F′ inFIG. 14B corresponds to a cross-sectional view obtainable by cuttingFIG. 16 along the chain line F-F′.

An active-matrix substrate includes gate wiring arranged in the rowdirection, source wiring arranged in the column direction, a pixelportion having pixel TFTs respectively provided in the vicinity ofcrossing points of the gate wiring and the source wiring, and a drivercircuit including an n-channel TFT and a p-channel TFT. The term “gatewiring” refers herein to a structure in which the gate wiring arrangedin the row direction is electrically connected to a gate electrode via acontact hole.

In a plane view of FIG. 16, a source wiring 839, a gate electrode 836,and a gate electrode 838 are formed in the identical layer. An electrodeextending from the gate electrode 836 and the gate electrode 838 alsofunctions as a capacitor electrode. A first interlayer insulating film(designated with reference numeral 864 in FIG. 14B) is formed to contactthe source wiring 839, the gate electrode 836, and the gate electrode838. A second interlayer insulating film (designated with referencenumeral 865 in FIG. 14B) is formed over the first interlayer insulatingfilm. Furthermore, a gate wiring 871, a capacitor connecting electrode873, a drain electrode 872, and a source connecting electrode 870 areformed on the second interlayer insulating film.

Since this is a transmission type liquid crystal electro-optical device,a pixel electrode 874 is formed so as to overlap the drain electrode872. The pixel electrode 874 is made of a transparent conductive film.The pixel electrode 874 is formed so as to overlap the capacitorconnecting electrode 873 and the drain electrode 872.

The gate wiring 871 is formed for the gate electrode 836 and the gateelectrode 838 via the first interlayer insulating film and the secondinterlayer insulating film. In the pixel structure shown in FIG. 16, thegate electrode 836 and the gate electrode 838 are formed in anisland-shaped pattern, and function not only as the gate electrode butalso as one of electrodes constituting a storage capacitor of theadjacent pixel, as described previously.

In other words, the storage capacitor of the pixel electrode 874 employsthe insulating film covering the island-shape semiconductor films 805and 806 as its dielectric. The pixel electrode 874 is electricallyconnected to the capacitor connecting electrode 873, and the capacitorconnecting electrode 873 is electrically connected to the island-shapedsemiconductor film 806. Thus, the island-shaped semiconductor film 806functions as a first capacitor electrode. The gate electrode 836 and thegate electrode 838 function as a second capacitor electrode.

Regions between the adjacent pixels can be light-shielded by mainlyallowing an end portion of the pixel electrode 874 to overlap with thesource wiring 839.

Manufacturing steps of the active-matrix substrate in accordance withthe present embodiment will be described with reference to FIGS. 12A to12C, 13A to 13C, 14A, and 14B.

As illustrated in FIG. 12A, base film 801 and 802 made of an insulatingfilm, such as a silicon oxide film, a silicon nitride film, or a siliconoxynitride film, are formed on a substrate 800 made of a glass such as abarium borosilicate glass or a alumino borosilicate glass, typically a#7059 glass, a #1737 glass or the like available from Corning Co. Forexample, a silicon oxynitride film 801 made from SiH₄, NH₃, and N₂O by aplasma CVD method is formed to have a thickness in the range from 10 to200 nm (preferably 90 to 100 nm), and similarly, a hydrogenated siliconoxynitride film 802 made from SiH₄ and N₂O is laminated thereon to havea thickness in the range from 90 to 200 nm (preferably 100 to 190 nm).Although the two-layered structure is employed in the presentembodiment, a single-layered film of the above-mentioned insulating filmmay be used. Alternatively, a structure in which the two or more layersof the above-mentioned insulating films are laminated may be used.

The island-shaped semiconductor films 803 to 806 are made of acrystalline semiconductor film formed from a semiconductor film havingan amorphous structure through a laser crystallization method or a knownthermal crystallization method. Thicknesses of these island-shapedsemiconductor films 803 to 806 are set in the range from 25 to 80 nm(preferably 30 to 60 nm). Although a constituent material of thecrystalline semiconductor film is not limited to the specific one, thefilm is preferably made of silicon, or a silicon germanium (SiGe) alloy.

In order to manufacture the crystalline semiconductor film by means ofthe laser crystallization method, an excimer laser of thepulse-oscillation type or the continuous-emission type, a YAG laser or aYVO₄ laser is used. In the case where these lasers are to be used, thelaser light emitted from a laser oscillator is converged in a linearshape by an optical system so that a semiconductor film is irradiatedwith the converged laser light. Although the crystallization conditionscan be appropriately set by an operator, in the case where an excimerlaser is to be used, a pulse oscillation frequency is set at 30 Hz, anda laser energy density is set in the range from 100 to 800 mJ/cm²(typically in the range from 200 to 300 mJ/cm²). In the case where a YAGlaser is to be used, a second harmonic wave is employed with a pulseoscillation frequency in the range from 1 to 10 kHz and a laser energydensity in the range from 300 to 600 mJ/cm² (typically in the range from390 to 900 mJ/cm²). The entire substrate is irradiated with the linearlyconverged laser light having a width of 100 to 1000 μm, for example 800μm, with an overlap ratio of the linear laser light in this case of 80to 98%.

As another manufacturing method of the crystalline semiconductor filmwhich forms an active layer of the TFT on the active-matrix substrate, amethod for obtaining a crystalline semiconductor film throughcrystallization by means of catalytic elements, as disclosed in JapanesePatent Application Laid-open No. Hei 7-130652, may be used.

Then, a gate insulating film 807 is formed to cover the island-shapedsemiconductor films 803 to 806. The gate insulating film 807 is formedof an insulating film containing silicon by a plasma CVD method or asputtering method to have a thickness in the range from 80 to 190 nm. Inthe present embodiment, the gate insulating film 807 is made of asilicon oxynitride film having a thickness of 120 nm. Of course, thegate insulating film is not limited to such a silicon oxynitride film,but alternatively, the other insulating film containing silicon may beformed in a single layer or in a laminated structure. For example, inthe case where a silicon oxide film is to be used, TEOS (tetraethylorthosilicate) is mixed with 0° by a plasma CVD method to form the filmwith the discharge at a high frequency (13.56 MHz) power density of 0.5to 0.8 W/cm² under conditions of a reaction pressure of 80 Pa and asubstrate temperature of 300 to 800° C. The silicon oxide film thusformed can be then provided with satisfactory characteristics as thegate insulating film by means of a thermal annealing at 800 to 900° C.

Thereafter, a first conductive film 808 and a second conductive film 809are formed on the gate insulating film 807 for forming the gateelectrode. In the present embodiment, the first conductive film 808 ismade of TaN with a thickness in the range from 90 to 100 nm, while thesecond conductive film 809 is made of W with a thickness in the rangefrom 100 to 300 nm.

In the case where a W film is to be formed, the film is formed by asputtering method with W being used as a target. Alternatively, the Wfilm can be formed through a thermal CVD method which employs tungstenhexafluoride (WF₆). In either case, the W film is required to have a lowresistivity in order to be used as the gate electrode, and therefore, itis preferable that the resistivity of the W film is equal to or lessthan 20 μΩcm. Although the resistivity of the W film can be decreased byenlarging crystal grains of the W film, the crystallization of the Wfilm is prevented when a large amount of impurity elements such asoxygen is contained in the W film, resulting in a larger resistivity.Thus, in the case where the W film is formed by a sputtering method, theresistivity in the range of 9 to 20 μΩcm can be realized by employing aW target having the purity of 99.9999% and paying sufficient attentionso as not to allow impurities to be mixed into the film from the vaporphase during the film deposition.

Although in the present embodiment, the first conductive film 808 ismade of TaN and the second conductive film 809 is made of W, both ofthese films may be formed of any element selected from the groupconsisting of Ta, W, Ti, Mo, Al, and Cu, or an alloy material or acompound material including the above-mentioned element as a maincomponent. Alternatively, a semiconductor film, typically apolycrystalline silicon film including impurity elements such asphosphorus doped thereto, may be used. As the combination other thanthat described in the present embodiment, the first conductive film maybe made of tantalum nitride (TaN) and the second conductive film may bemade of Al, or the first conductive film may be made of tantalum nitride(TaN) and the second conductive film may be made of Cu.

Thereafter, masks 811 to 816 made of a resist are formed, and a firstetching process is performed (see FIG. 12B) to form electrodes andlines. In the present embodiment, an ICP (Inductively Coupled Plasma)etching method is employed in which a mixed gas of CF₄ and Cl₂ is usedas an etching gas and an RF (13.56 MHz) power of 900 W is applied to acoil-shaped electrode under a pressure of 1 Pa to generate plasma forperforming the etching process. An RF (13.56 MHz) power of 100 W is alsoapplied to a substrate side (sample stage) so that a substantiallynegative self-biased voltage is applied. In the case where CF₄ and Cl₂are mixed, both the W film and the Ta film are etched away to the sameextent.

In the above-mentioned etching conditions, the first conductive layerand the second conductive layer can be formed to have end portions in atapered-shape having a tapered angle of 15 to 85° due to an effect ofthe bias voltage to be applied to the substrate side by forming theresist masks in an appropriate shape. In order to perform the etchingprocess without leaving any etching residue on the gate insulating film,it is preferable to increase an etching time period by approximately 10to 20%. Since a selection ratio of a silicon oxynitride film against a Wfilm is in the range from 2 to 4 (typically 3), a surface on which thesilicon oxynitride film is exposed is etched away by about 20 to 90 nmby an overetching process. Thus, by the first etching process,first-shape conducting layers 820 to 825 (first conducting layers 820 ato 825 a and second conducting layers 820 b to 825 b) made of the firstconducting layer and the second conducting layer are formed. Referencenumeral 818 denotes a gate insulating film, and a region which is notcovered with the first-shape conducting layers 820 to 825 is etched awayby about 20 to 90 nm so that a thinned region is formed.

Thereafter, as shown in FIG. 12C, a second etching process is performed.An ICP etching method is similarly employed in which a mixed gas of CF₄,Cl₂ and O₂ is used as an etching gas and an RF power (13.56 MHz) of 900W is applied to a coil-shape electrode under a pressure of 1 Pa togenerate plasma for performing the etching process. An RF (13.56 MHz)power of 90 W is applied to a substrate side (sample stage) so that aself-biased voltage lower than that in the first etching process isapplied. Under such conditions, the W film is anisotropically etched andTaN constituting the first conductive layers is anisotropically etchedat a lower etching rate so as to form second-shape conducting layers 834to 839 (first conducting layers 834 a to 839 a and second conductinglayers 834 b to 839 b). Reference numeral 875 denotes a gate insulatingfilm, and a region which is not covered with the second-shape conductinglayers 834 to 839 is further etched away by about 20 to 90 nm so that athinned region is formed.

Then, a first doping process is performed to add an impurity elementproviding the n-type conductivity with a middle acceleration at a lowconcentration. As a doping method, an ion-doping method or an ionimplantation method may be used. An element belonging to Group 15,typically phosphorus (P) or arsenic (As), can be used as the impurityelement providing the n-type conductivity, and in the presentembodiment, phosphorus (P) is used. In this case, the conducting layers834 to 838 function as a mask against the impurity element providing then-type conductivity to form first impurity regions 828 to 832 in aself-alignment manner. In this specification, impurity regions coveredwith TaN as the first conducting layers (834 a to 838 a) arespecifically referred to as the first impurity regions (828 to 832),while impurity regions that are not covered with TaN as the firstconducting layers (834 a to 838 a) are specifically referred to as thesecond impurity regions (841 to 845). The concentration of the firstimpurity regions (828 to 832) is set to be in the range from 2×10¹⁶ to5×10¹⁹ atoms/cm³.

As shown in FIG. 13A, the gate conductive layers is etched by using theTaN constituting the first conducting layers (834 a to 839 a) as masks.A region in which the first insulating film and the gate insulating filmdo not overlap with each other is etched away. Thereafter, the resists811 to 816 shown in FIG. 12B are peeled off by a peeling liquidcontaining N-methyl-2-pyrrolidone (NMP) as its main component.

Then, as shown in FIG. 13B, resists 846 to 848 are formed and a seconddoping process is performed. In this case, an impurity element providingthe n-type conductivity is added into the island-shape semiconductorfilms with a high acceleration at a low concentration. Thereafter, animpurity element providing the n-type conductivity is added into theisland-shape semiconductor films with a low acceleration at a highconcentration. Thus, third impurity regions 850 to 858 as new impurityregions are formed at the end portions of the second impurity regions(denoted with reference numerals 841 to 845 in FIG. 12C) formed in theisland-shape semiconductor film. Fourth impurity regions (866 and 867)having the impurity concentration lower than that in the third impurityregions are formed in a region to which the n-type impurity element hasbeen added via the gate insulating film.

At this stage, the concentration of the first impurity regions (828,830, 832) is set in the range from 2×10¹⁶ to 5×10¹⁹ atoms/cm³. Inaddition, the concentration of the second impurity regions (841, 843,845) is set in the range from 1×10¹⁶ to 5×10¹⁸ atoms/cm³. Theconcentration of the n-type impurities of the third impurity regions(850 to 858) is set in the range from 1×10²⁰ to 1×10²² atoms/cm³. Theconcentration of the n-type impurities of the fourth impurity regions(866 and 867) is set to be lower than the concentration in the thirdimpurity regions but higher than the concentration in the secondimpurity regions.

Then, as shown in FIG. 13C, after the resists 846 to 848 are peeled off,a resist 859 and a resist 860 are formed. A third doping process isperformed with the resist 859 and the resist 860 being employed asmasks. Thus, impurity elements providing the p-type conductivity areintroduced into the island-shape semiconductor films to form a p-channelTFT. Fifth impurity regions (861 and 876) and sixth impurity regions 862and 863 are formed in the island-shape semiconductor film 803. At thisstage, the island-shape semiconductor layers 804 to 806 in which ann-channel TFT is to be formed are entirely covered with resists 859 and860 as masks. The fifth impurity regions (861 and 876) and the sixthimpurity regions 862 and 863 are provided with the impurity elementsproviding the p-type conductivity doped therein at concentrationsdifferent from each other. In the third doping process, an ion dopingmethod employing diborane (B₂H₆) is used. The concentration of theimpurity elements providing the p-type conductivity is set to be anamount sufficient for inverting the n-channel type impurity region intothe p-channel type impurity region.

In accordance with the above-described process, the impurity regions areformed into the respective island-shape semiconductor films. Theconducting layers 834 to 836 and the conducting layer 838 that overlapwith the island-shape semiconductor films function as the gateelectrodes of the TFTs. Reference numeral 839 denotes a source wiringand reference numeral 837 denotes a capacitor electrode.

Thereafter, as shown in FIG. 14A, a process for activating the impurityelements added to the respective island-shape semiconductor films isperformed. This process is performed by a thermal annealing method whichemploys an annealing furnace. Alternatively, a laser annealing method ora rapid thermal annealing method (RTA method) can be applied. In thethermal annealing method, the process is performed at a temperature inthe range of 600 to 900° C., typically 700 to 800° C., in a nitrogenatmosphere with an oxygen concentration of 1 ppm or less, preferably 0.1ppm or less. In the present embodiment, the thermal treatment isperformed at a temperature of 900° C. for 4 hours. However, in the casewhere wiring materials used for the component designated with referencenumerals 834 to 839 do not have a sufficient resistance against heat, itis preferable to perform activation after an interlayer insulating film(containing silicon as a main component) is formed in order to protectthe lines or the like.

Furthermore, a thermal process is performed at 300 to 890° C. for 1 to12 hours in an atmosphere containing hydrogen of 3 to 100% to perform aprocess for hydrogenating the island-shape semiconductor layers. In thisprocess, dangling bonds in the semiconductor layers are terminated withhydrogens thermally excited. A plasma hydrogenation (in which hydrogenexcited by a plasma are used) may be performed as other means forhydrogenation.

Then, as shown in FIG. 14B, a first interlayer insulating film 864 isformed on the gate electrode and the gate insulating film. The firstinterlayer insulating film may be formed of a silicon oxide film, asilicon oxynitride film, a silicon nitride film, or a laminated layeredfilm in which these films are combined. In either case, the firstinterlayer insulating film 864 is formed of an inorganic insulatingmaterial. A thickness of the first interlayer insulating film 864 is setin the range from 100 to 200 nm.

In this case, when a silicon oxide film is to be used, TEOS (TetraethylOrthosilicate) is mixed with 0, in a plasma CVD method with a reactionpressure of 80 Pa and a substrate temperature of 300 to 800° C. in whichthe film is formed by discharge with a high frequency (176 MHz) powerdensity of 0.5 to 0.8 W/cm². In the case where a silicon oxynitride filmis to be used, a silicon oxynitride film may be formed from SiH₄, N₂O,and NH₃ by a plasma CVD method, or formed from SiH₄ and N₂O. Thefabrication conditions in this case can be such that a reaction pressureis in the range from 20 to 200 Pa, a substrate temperature is in therange from 300 to 800° C., and a high frequency (60 MHz) power densityis in the range from 0.1 to 1.0 W/cm². Alternatively, a siliconoxynitride film formed from SiH₄, N₂O, and H₂ may be used. A siliconnitride film can be also formed similarly from SiH₄ and NH₃ by a plasmaCVD method. In the present embodiment, the first interlayer insulatingfilm 864 is formed of a silicon oxynitride film to have a thickness inthe range from 100 to 200 nm.

Thereafter, a second interlayer insulating film 865 made of an organicinsulating material is formed so as to have an average thickness in therange from 1.0 to 2.0 μm. As the organic resin material, polyimide,acrylic, polyamide, polyimide-amide, BCB (benzocyclobutene) or the likecan be used. For example, in the case where a polyimide which isthermally polymerized after being applied onto a substrate is to beused, the material is formed by being baked in a clean oven at 300° C.In the case where an acrylic resin is to be used, a two-liquid typematerial is used. A main component and a curing agent are mixed and theresultant mixture is applied onto the entire substrate by a spinner, andthereafter, a preliminary heating at 80° C. for 60 seconds is performedwith a hot plate and the baking is further performed in a clean oven at290° C. for 60 minutes.

By thus forming the second interlayer insulating film with an organicinsulating material, a surface can be planarized in a satisfactorymanner. In addition, since the organic resin material in general has alow dielectric constant, a parasitic capacitance can be reduced.However, the organic resin material exhibits water-absorbingcharacteristics, rendering the material inappropriate as a protectionfilm. Accordingly, it is necessary to be combined with a silicon oxidefilm, a silicon oxynitride film, a silicon nitride film, or the likeformed as the first interlayer insulating film 864, as in the presentembodiment.

Thereafter, a photo mask is used to form a resist mask in apredetermined pattern, and contact holes are formed to reach a sourceregion or a drain region formed in the respective island-shapesemiconductor films. The contact holes are formed by a dry etchingmethod. In this case, a mixture gas of CF₄, O₂, and He is used as anetching gas to first etch the second interlayer insulating film 865 madeof the organic resin material, and thereafter, CF₄ and O₂ are then usedas an etching gas to etch the first interlayer insulating film 864.Furthermore, the etching gas is switched into CHF₃ in order to increasea selection ratio against the island-shape semiconductor layers and thegate insulating film is etched. Thus, the contact holes can be formed ina satisfactory manner.

Thereafter, a conducting metal film is formed by a sputtering method ora vapor-deposition method, and a pattern of a photo mask is formed witha resist being used by a mask, so that the source wiring 866 and 867,the drain lines 868 and 869, the drain electrode 872, the sourceconnecting electrode 870, the capacitor connecting electrode 873, andthe gate wiring 871 are formed by an etching process.

At this stage, the drain electrode 872 functions by being electricallyconnected to the pixel electrode 874 to be described later. Thecapacitor connecting electrode 873 applies an electrical potential tothe island-shape semiconductor layer 806 which is to function as anelectrode of the storage capacitor 904. The gate wiring 871 iselectrically connected to the gate electrode 836 and the gate electrode838 by the contact hole, as described with reference to the top planview in FIG. 16. It should be noted that the storage capacitor 904 inthe present embodiment exists in the same pixel as the pixel electrode874.

In FIG. 14, a Ti film as the conducting metallic film is formed to havea thickness in the range from 90 to 190 nm so as to form a contact withthe source region or the drain region in the island-shape semiconductorfilm, and aluminum (Al) is further overlaid on the Ti film to have athickness in the range from 300 to 800 nm, and thereafter, a Ti film ora titanium nitride (TiN) film is formed to have a thickness in the rangefrom 100 to 200 nm, so that a three-layered structure is obtained. Insuch a structure, the pixel electrode 874 to be described later is tocontact only the Ti film which constitutes the drain electrode 872 andthe capacitor connecting electrode 873. As a result, the transparentconductive film can be prevented from being reacted with Al.

Thereafter, a transparent conductive film is formed over the entiresurface, and the pixel electrode 874 is formed by a patterning processand an etching process that employ a photo mask. The pixel electrode 874is formed on the interlayer insulating film 865 so as to includeportions overlapping the drain electrode 872 in the pixel TFT 903 andthe capacitor connecting electrode 873 of the storage capacitor 904,thereby resulting in a connection structure being formed. Thus, theisland-shape semiconductor film 806 functioning as an electrode of thestorage capacitor 904 is electrically connected to the pixel electrode874.

As a material for the transparent conductive film, indium oxide (In₂O₃),indium tin oxide (In₂O₃—SnO₂; an ITO film) alloy or the like can beformed by a sputtering method, a vacuum evaporation method or the like.An etching process of such a material is performed by means of asolution of the hydrochloric acid type. However, especially in anetching process of an ITO film, etching residue are likely to begenerated. Thus, in order to improve the etching processibility, anindium oxide zinc oxide alloy (In₂O₃—ZnO) may be used. The indium oxidezinc oxide alloy has excellent surface smoothness and satisfactorythermal stability in contrast to an ITO film, so that even in the casewhere Al is used for the drain line 872 and the capacitor connectingline 873, a corrosive reaction with Al which is to contact on thesurface can be prevented. Similarly, zinc oxide (ZnO) is also anappropriate material, and furthermore, other materials, such as zincoxide to which gallium (Ga) is added for improving the transmittance ofvisible light or a conductivity (indicated as ZnO:Ga), may be used.

When the hydrogenation process is performed under this condition,preferable effects with respect to improvements in the TFTcharacteristics can be obtained. For example, it is preferable toperform a thermal treatment in an atmosphere containing hydrogen of 3 to100% at 300 to 890° C. for 1 to 12 hours. Alternatively, the sameresults can be achieved also by a plasma hydrogenation method. It isdesirable to reduce the defect density in the island-shape semiconductorfilms 803 to 806 at 10¹⁶/cm³ or lower, and the above purpose can berealized by adding hydrogen at about 0.01 to 0.1 atomic %.

As described in the above, the driver circuit portion 905 (including thep-channel type TFT 901 and the n-channel type TFT 902), the pixel TFT903, and the storage capacitor 904 can be formed on the same substrate.In the present specification, such a substrate is referred to as theactive-matrix substrate.

In accordance with the fabricating process as described in the presentembodiment, the number of the photo masks required for fabricating theactive-matrix substrate can be set at seven (i.e., the island-shapesemiconductor layer pattern, a first wiring pattern [the gate electrode,the source wiring, and the capacitor wiring], the n-channel region maskpattern, the p-channel region mask pattern, the contact hole pattern,the second line pattern [the source wiring, the drain line, the sourceconnecting electrode, the drain electrode, the capacitor connectingelectrode, and the gate wiring], and the pixel electrode pattern).

Then, as shown in FIG. 15, an ITO film 908 as the transparent conductivefilm is formed on a transparent insulating substrate 910 to have athickness of 120 nm. In order to prevent any parasitic capacitance frombeing generated, a portion of the ITO film over the driver circuitportion is removed by a patterning process and an etching processemploying a photo mask. The ITO film 908 functions as an opposingelectrode. In the present specification, such a substrate is referred toas a opposing substrate.

In order to realize a color display, color filters are formed on theopposing substrate. More specifically, the three primary colors in theadditive color mixture, i.e., red, blue and green, are arranged inparallel. With this structure, a better color purity can be obtained ascompared to the case where the subtractive color filters of cyan,magenta, and yellow are arranged in parallel.

An alignment film 907 and a polarizing film 909 are formed on theactive-matrix substrate and on the opposing substrate, respectively, toeach have a thickness of 80 nm. As these polarizing films. SE7792(Nissan Chemical) is used.

Spacers (not illustrated) are scattered by a wet scattering method or adry scattering method. Spacers may be formed by forming a photosensitiveorganic resin at predetermined positions by patterning. The height ofthe spacers is set at 4 μm.

Thereafter, a sealing member (not illustrated) is provided on theopposing substrate by a dispense drawing method. After the sealingmember is applied, the sealing member is baked at 90° C. for about 0.5hours.

After the above-mentioned process steps, the active-matrix substrate andthe opposing substrate are adhered to each other. The active-matrixsubstrate and the opposing substrate are arranged so that the respectiverubbing directions thereof cross with each other at the right angle uponthe adhesion. A pressure of 0.3 to 1.0 kgf/cm² is applied to a pair ofthe thus adhered substrates over the entire substrate surface in thedirection perpendicular to the substrate surface. Simultaneously, aheating process is performed in a clean oven at 160° C. for about twohours so that the sealing member is allowed to be cured, therebyresulting in the active-matrix substrate and the opposing substratebeing securely adhered.

Then, after the adhered pair of substrates is cooled down, it is dividedby means of a scriber and a breaker.

Liquid crystal 911 is then injected by a vacuum injection method. Apanel after being divided is provided within a vacuum chamber. After thevacuum chamber is evacuated by a vacuum pump to a vacuum condition ofabout 1.33×10⁻⁵ to 1.33×10⁻⁷ Pa, an injection port is immersed into aliquid crystal saucer filled with the liquid crystal. As the liquidcrystal, ZLI4792 (Merk) is used.

Then, when the vacuum chamber in the vacuum condition is graduallyleaked by means of nitrogen so as to return to an atmospheric pressure,the liquid crystal is injected through the injection port of a liquidcrystal panel due to a pressured difference between the air pressure inthe panel and the atmospheric pressure as well as the capillary actionof the liquid crystal, so that the liquid crystal gradually moves from aside closer to the injection port toward the opposite side, therebycompleting the injection process.

After confirming that the inside of the sealing member is filled withthe liquid crystal, a pressure is applied onto both surfaces of theliquid crystal panel. After 15 minutes, extra liquid crystal material iswiped away. An UV-curable resin (not illustrated) is applied to theinjection port while the pressure being still applied, and then theapplied pressure is reduced. At this stage, the UV-curable resin entersinto the inside. The UV-curable resin is irradiated with UV rays (4 to10 mW/cm², for 120 seconds) under this condition, so that the UV-curableresin is allowed to be cured, thereby resulting in the injection portbeing sealed.

Thereafter, the liquid crystal existing on the substrate surface and onthe end surface is washed out by an organic solvent, for example,acetone and ethanol. The liquid crystal is then allowed to bere-oriented at 130° C. for about 0.5 hour.

A flexible print circuit (FPC) is then connected, and polarizing platesare adhered to the active-matrix substrate and the opposing substrate,respectively, thereby completing a TN-type liquid crystalelectro-optical device.

In the present embodiment, the transmission type liquid crystalelectro-optical device has been fabricated. Furthermore, by combiningthe back light as the illumination apparatus in accordance with thepresent invention as disclosed in Embodiment Mode 1 with thetransmission type liquid crystal electro-optical device in the presentembodiment, power consumption can be reduced while an image with auniform in-plane brightness distribution can be recognized by a viewer.

In the present embodiment, by patterning the drain electrode 872 in FIG.14B as the pixel electrode in a wider area, a reflection type liquidcrystal electro-optical device can be fabricated. By employing the frontlight as the illumination apparatus in accordance with the presentinvention as disclosed in Embodiment Mode 2, power consumption can bereduced while an image with a uniform in-plane brightness distributioncan be recognized by a viewer.

Embodiment 2

The lighting apparatus formed by implementing the present invention canbe used in a variety of electro-optical devices. Namely, the presentinvention can be implemented for all electronic equipment, whichincorporates this type of electro-optical device in a display portion.The following can be given as such electronic equipment: a personalcomputer, a digital camera, a video camera, a portable informationterminal (such as a mobile computer, a portable telephone, or anelectronic book) and a navigation system. Some examples of these areshown in this embodiment.

FIG. 17A shows a portable telephone, and contains components such as amain body 9001, an audio output portion 9002, an audio input portion9003, a display portion 9004, operation switches 9005, and an antenna9006. The present invention can be applied to the display portion 9004having an active matrix substrate.

FIG. 17B shows a video camera and contains components such as a mainbody 9101, a display portion 9102, an audio input portion 9103,operation switches 9104, a battery 9105, and an image receiving portion9106. The present invention can be applied to the display portion 9102.

FIG. 17C shows a mobile computer or a portable information terminal andcontains components such as a main body 9201, a camera portion 9202, animage receiving portion 9203, operation switches 9204, and a displayportion 9205. The present invention can be applied to the displayportion 9205.

FIG. 17D shows a head mount display and contains components such as amain body 9301, a display portion 9302, and an arm portion 9303. Thepresent invention can be applied to the display portion 9302.

FIG. 17E shows a television and contains components such as a main body9401, a speaker 9402, a display portion 9403, a receiving device 9404,an amplifier 9405 and so forth. The present invention can be applied toa display portion 9403.

FIG. 17F shows a portable electronic book that is composed of a mainbody 9501, display devices 9502, 9503, a memory medium 9504, anoperation switch 9505 and an antenna 9506. The book is used to displaydata stored in a mini-disk (MD) or a DVD, or a data received with theantenna. The display devices 9502, 9503 are direct-vision type displaydevices and the present invention can be applied to the display devices9502, 9503.

FIG. 18A shows a personal computer and contains components such as amain body 9601, an image input portion 9602, a display portion 9603, anda keyboard 9604. The present invention can be applied to the displayportion 9603.

FIG. 18B shows a player which uses a recording medium with a programrecorded therein (hereinafter referred to as recording medium) andcontains components such as main body 9701, a display portion 9702, aspeaker portion 9703, a recording medium 9704, and operation switches9705. Note that a DVD (Digital Versatile Disk), CD, etc. is used as arecording medium for this player, and that appreciation of music or amovie or performing games or the Internet can be done. The presentinvention can be applied to the display device 9702.

FIG. 18C shows a digital camera and contains components such as a mainbody 9801, a display portion 9802, an eye piece portion 9803, operationswitches 9804, and an image receiving portion (not shown in the figure).The present invention can be applied to the display portion 9802.

Thus, as described in the above, in accordance with the presentinvention, a point light source such as a light emitting diode can beconverted into a line light source by means of a linear light guidingplate, and furthermore, the line light source can be converted into aplane light source by means of a plane-like light guiding plate. By thusconverting the point light source into the plane light source in the twostages, a uniform plane light source can be obtained. In this case, itis only required, to provide the light emitting diode on a side surfaceof the linear light guiding plate, and therefore, the uniform planelight source can be obtained even when only a small number of the lightemitting diodes are used. Furthermore, by designing the lightpropagation direction by means of the linear light guiding plate, alight source having excellent in-plane uniformity can be obtained.

In accordance with the present invention, the plane light source can beobtained from a piece of plate-like light guiding plate by allowinglight emitted from the point light source to be incident on at least twoof the side surfaces of the plate-like light guiding plate.

In addition, in accordance with the present invention, an illuminationapparatus which is more suitable to portable terminal applications canbe fabricated by employing a light emitting diode that has small powerconsumption and is a small-sized point light source.

1. An illumination apparatus comprising: a first light guiding plateincluding a first surface, a second surface, a third surface, and afourth surface; a second light guiding plate including a side surfaceand a lower surface; a reflecting member; and a point light source,wherein a light emitted from said point light source is incident on saidfirst surface and exits through said second surface, wherein said lightexiting through said second surface is incident on said side surface ofsaid second light guiding plate, and exits through said lower surface ofsaid second light guiding plate, wherein said second surface isperpendicular to said third and fourth surfaces, wherein said third andfourth surfaces are positioned to face each other, and whereinprojections are formed on said lower surface of said second lightguiding plate.
 2. The illumination apparatus according to claim 1,wherein said first light guiding plate has a shape of a rectangularprism.
 3. The illumination apparatus according to claim 1, wherein inkdots are provided on a fifth surface of said first light guiding plateopposite to said second surface of said first light guiding plate. 4.The illumination apparatus according to claim 3, wherein said ink dotsare provided at a lower density at a region closer to said point lightsource then at a region further from said point light source.
 5. Anillumination apparatus comprising: a first light guiding plate includinga first surface, a second surface, a third surface, and a fourthsurface; a second light guiding plate including a side surface and alower surface; a point light source; a reflecting member; and anelectro-optical device, wherein a light emitted from said point lightsource is incident on said first surface and exits through said secondsurface, wherein said light exiting through said second surface isincident on said side surface of said second light guiding plate, andexits through said lower surface of said second light guiding plate,wherein said light exiting through said lower surface of said secondlight guiding plate is incident on said electro-optical device, whereinsaid second surface is perpendicular to said third and fourth surfaces,wherein said third and fourth surfaces are positioned to face eachother, and wherein projections are formed on said lower surface of saidsecond light guiding plate.
 6. The illumination apparatus according toclaim 5, wherein said first light guiding plate has a shape of arectangular prism.
 7. The illumination apparatus according to claim 5,wherein ink dots are provided on a side surface of said first lightguiding plate.
 8. The illumination apparatus according to claim 7,wherein said ink dots are provided at a lower density at a region closerto said point light source then at a region further from said pointlight source.
 9. An illumination apparatus comprising: a first lightguiding plate; a second light guiding plate including a side surface anda lower surface; a point light source; and at least first and second inkdots provided on a side surface of said first light guiding plate,wherein a light emitted from said point light source is incident on saidfirst light guiding plate, and exits through said first light guidingplate, wherein said light exiting through said first light guiding plateis incident on said side surface of said second light guiding plate, andexits through said lower surface of said second light guiding plate,wherein said first ink dot is nearer to said point light source thansaid second ink dot, wherein a size of said second ink dot is largerthan a size of said first ink dot, and wherein projections are formed onsaid lower surface of said second light guiding plate.
 10. Theillumination apparatus according to claim 9, wherein said first lightguiding plate has a shape of a rectangular prism.
 11. The illuminationapparatus according to claim 1, wherein said reflecting member coverssaid third and fourth surfaces.
 12. The illumination apparatus accordingto claim 5, wherein said reflecting member covers said third and fourthsurfaces.